Display medium driver, non-transitory computer-readable medium, display device, and method of driving display medium

ABSTRACT

A display medium driver includes a translucent display substrate, a rear substrate that is opposed to the display substrate with a gap interposed therebetween, a dispersion medium enclosed between the substrates, a first particle group dispersed in the dispersion medium so as to migrate by applying a first voltage across the substrates, and a second particle group dispersed in the dispersion medium so as to migrate by applying a second voltage across the substrates, the driver including a setting unit setting a voltage value and a voltage application time of the first voltage with which the first particle group does not migrate at the time of causing the second particle group to migrate depending on a display density of the second particle group and a voltage application unit first applying the first voltage across the substrates and then applying the second voltage across the substrates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of application Ser. No. 13/209,103 filed Aug. 12,2011, which claims priority to Japanese Patent Application No.2011-000528 filed Jan. 5, 2011. The disclosure of the prior applicationsis hereby incorporated by reference herein in its entirety.

BACKGROUND Technical Field

The present invention relates to a display medium driver, anon-transitory computer-readable medium, a display device, and a methodof driving a display medium.

SUMMARY

According to an aspect of the invention, there is provided a displaymedium driver including a display substrate that has translucency, arear substrate that is opposed to the display substrate with a gapinterposed therebetween, a dispersion medium that is enclosed betweenthe display substrate and the rear substrate, plural types of particlegroups that are dispersed in the dispersion medium, that are enclosedbetween the substrates so as to migrate between the substrates dependingon an electric field formed between the substrates, and that aredifferent from each other in color and charged polarity, the driverincluding: a setting unit that sets a voltage value and a voltageapplication time of a first voltage with which a first particle groupamong the plural types of particle groups does not migrate at the timeof causing a second particle group to migrate depending on a displaydensity of the second particle group when the second particle group ofwhich the absolute value is smaller than a first threshold value iscaused to migrate after the first particle group is caused to migrate byapplying the first voltage equal to or greater than the first thresholdvalue across the substrates; and a voltage application unit that firstapplies the first voltage set by the setting unit across the substratesand then applies the second voltage across the substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described indetail based on the following figures, wherein:

FIGS. 1A and 1B are diagrams schematically illustrating a displaydevice;

FIG. 2 is a diagram illustrating threshold characteristics of migrationparticles;

FIG. 3 is a diagram illustrating the relationship between an electricfield intensity and a driving time;

FIG. 4 is a diagram illustrating the relationship between a drivingenergy and a threshold electric field intensity;

FIG. 5 is a diagram illustrating the relationship between an electricfield intensity and a driving speed;

FIG. 6 is a diagram illustrating threshold characteristics of migrationparticles;

FIGS. 7A to 7C are diagrams illustrating migrating conditions ofmigration particles;

FIGS. 8A to 8D are diagrams illustrating migrating conditions ofmigration particles;

FIG. 9 is a diagram illustrating threshold characteristics of migrationparticles;

FIG. 10 is a diagram illustrating the relationship between a drivingenergy and a threshold electric field intensity;

FIG. 11 is a table illustrating the relationship between thresholdcharacteristics of magenta particles and the density and mixed color ofcyan particles;

FIGS. 12A to 12C are diagrams illustrating an order in which a voltageis applied;

FIG. 13 is a diagram illustrating threshold characteristics of migrationparticles;

FIG. 14 is a table illustrating the relationship between thresholdcharacteristics of magenta particles and the density and mixed color ofcyan particles;

FIG. 15 is a diagram illustrating an order in which a voltage isapplied;

FIGS. 16A and 16B are diagrams illustrating an order in which a voltageis applied;

FIGS. 17A to 17C are diagrams illustrating an order in which a voltageis applied;

FIG. 18 is a flowchart illustrating the flow of processes performed by acontrol unit;

FIG. 19 is a diagram illustrating threshold characteristics of migrationparticles;

FIG. 20 is a table illustrating the relationship between a voltage in asecond stroke of magenta particles and the density and mixed color ofcyan particles;

FIG. 21 is a table illustrating the relationship between a voltage in asecond stroke of magenta particles and the density and mixed color ofcyan particles;

FIG. 22 is a table illustrating the relationship between a voltage in asecond stroke of magenta particles and the density and mixed color ofcyan particles; and

FIG. 23 is a table illustrating the relationship between a drivingcondition and a density in a second stroke of cyan particles.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the invention will be describedwith reference to the accompanying drawings. Elements having the sameoperation and function are referenced by the same reference numerals andsigns in the entire drawings, and the description may not be repeated.For the purpose of facilitating the explanation, the exemplaryembodiments will be described by focusing on a cell.

Particles of cyan are referred to as cyan particles C, particles ofmagenta are referred to as magenta particles M, particles of yellow arereferred to as yellow particles Y, and the particles and particle groupsare referenced by the same signs (reference signs).

FIG. 1A schematically illustrates a display device according to anexemplary embodiment of the invention. The display device 100 includes adisplay medium 10 and a driver 20 driving the display medium 10. Thedriver 20 includes a voltage application unit 30 that applies a voltageacross a display electrode 3 and a rear electrode 4 of the displaymedium 10 and a control unit 40 that controls the voltage applicationunit 30 on the basis of image information of an image to be displayed bythe display medium 10.

In the display medium 10, the display substrate 1 having translucencyand serving as an image display surface and the rear substrate 2 servingas a non-display surface are opposed to each other with a gap interposedtherebetween.

Spacer members 5 that maintain the substrates 1 and 2 with apredetermined gap and that partition the space between the substratesinto plural cells are provided.

A cell represents a region surrounded with the rear substrate 2 having arear electrode 4 formed thereon, the display substrate 1 having adisplay electrode 3 formed thereon, and the spacer members 5. In thecell, a dispersion medium 6 containing, for example, an insulatingliquid and a first particle group 11, a second particle group 12, and awhite particle group 13 which are dispersed in the dispersion medium 6are enclosed.

The first particle group 11 and the second particle group 12 aredifferent from each other in color and charged polarity and have acharacteristic in which the first particle group 11 and the secondparticle group 12 independently migrate by applying a voltage equal toor greater than a predetermined threshold voltage across the pair ofelectrodes 3 and 4. On the other hand, the white particle group 13 is aparticle group that has a smaller amount of electric charge than thoseof the first particle group 11 and the second particle group 12 and doesnot migrate to any electrode even when a voltage with which the firstparticle group 11 and the second particle group 12 migrate to anyelectrode is applied across the electrodes.

By mixing a coloring agent into the dispersion medium, white other thanthe colors of the migration particles may be displayed.

The driver 20 (the voltage application unit 30 and the control unit 40)causes the particles groups 11 and 12 to migrate by applying a voltagecorresponding to a color to be displayed across the display electrode 3and the rear electrode 4 of the display medium 10, and attracts theparticle groups to any one of the display substrate 1 and the rearsubstrate 2 depending on the charged polarities.

The voltage application unit 30 is electrically connected to the displayelectrode 3 and the rear electrode 4. The voltage application unit 30 isconnected to the control unit 40 so as to transmit and receive signalsthereto and therefrom.

As shown in FIG. 1B, the control unit 40 includes, for example, acomputer 40. In the computer 40, a central processing unit (CPU) 40A, aread only memory (ROM) 40B, a random access memory (RAM) 40C, anonvolatile memory 40D, and an input and output interface (I/O) 40E areconnected to each other via a bus 40F. The voltage application unit 30is connected to the I/O 40E. In this case, a program causing thecomputer 40 to execute a process of instructing the voltage applicationunit 30 to apply a voltage necessary for displaying various colors iswritten to, for example, the nonvolatile memory 40D and is read andexecuted by the CPU 40A. The program may be provided through the use ofa recording medium such as a CD-ROM.

The voltage application unit 30 is a voltage applying device applying avoltage across the display electrode 3 and the rear electrode 4, andapplies a voltage across the display electrode 3 and the rear electrode4 under the control of the control unit 40.

In this exemplary embodiment, for example, it is assumed that the rearelectrode 4 is grounded and a voltage is applied to the displayelectrode 3.

FIG. 2 illustrates the relationship (threshold characteristics) betweenthe electric field intensity (V/μm) to be applied across the substratesand the display density based on the particle groups when the rearelectrode 4 is grounded (0 V) and a voltage is applied to the displayelectrode 3. In FIG. 2, the threshold characteristic of cyan particles Cis represented by 50C and the threshold characteristic of magentaparticles M is represented by 50M. In this exemplary embodiment, forexample, it is assumed that the magenta particles M are chargednegatively and the cyan particles C are charged positively.

As shown in FIG. 2, the electric field intensity (the threshold electricfield intensity) with which the negatively-charged magenta particles Mclose to the rear substrate 2 start the migration to the displaysubstrate 1 is +V_(ML) and the electric field intensity (the thresholdelectric field intensity) with which all the magenta particles M end themigration to the display substrate 1 is +V_(MH). The electric fieldintensity (the threshold electric field intensity) with which themagenta particles M close to the display substrate 1 start the migrationto the rear substrate 2 is −V_(ML) and the electric field intensity (thethreshold electric field intensity) with which all the magenta particlesM end the migration to the rear substrate 2 is −V_(MH).

Therefore, the magenta particles M close to the rear substrate 2 startthe migration to the display substrate 1 by applying the electric fieldintensity equal to or greater than +V_(ML) across the substrates, andall the magenta particles M migrate to the display substrate 1 byapplying the electric field intensity equal to or greater than +V_(MH)across the substrates. The magenta particles M close to the displaysubstrate 1 start migration to the rear substrate 2 by applying theelectric field intensity equal to or less than −V_(ML) across thesubstrates, and all the magenta particles M migrate to the rearsubstrate 2 by applying the electric field intensity equal to or lessthan −V_(MH) across the substrates.

The electric field intensity (the threshold electric field intensity)with which the cyan particles C close to the rear substrate 2 start themigration to the display substrate 1 is −V_(CL) and the electric fieldintensity (the threshold electric field intensity) with which all thecyan particles C end the migration to the display substrate 1 is−V_(CH). The electric field intensity (the threshold electric fieldintensity) with which the cyan particles C close to the displaysubstrate 1 start the migration to the rear substrate 2 is +V_(CL) andthe electric field intensity (the threshold electric field intensity)with which all the cyan particles C end the migration to the rearsubstrate 2 is +V_(CH).

Therefore, the cyan particles C close to the rear substrate 2 start themigration to the display substrate 1 by applying the electric fieldintensity equal to or less than −V_(CL) and all the cyan particles Cmigrate to the display substrate 1 by applying the electric fieldintensity equal to or less than −V_(CH) across the substrates. The cyanparticles C close to the display substrate 1 start the migration to therear substrate 2 by applying the electric field intensity equal to orgreater than −V_(CL), and all the cyan particles C migrate to the rearsubstrate 2 by applying the electric field intensity equal to or greaterthan +V_(CH) across the substrates.

Here, the relationship between the electric field intensity and theparticle driving time (the particle migrating time) is the same as shownin FIG. 3. In FIG. 3, the characteristic indicating the relationshipbetween the electric field intensity and the driving time of theparticles of the magenta particles M is represented by thecharacteristic 52M and the characteristic indicating the relationshipbetween the electric field intensity and the driving time of the cyanparticles C is represented by the characteristic 52C. As shown in FIG.3, as the electric field intensity applied across the substratesincreases, the driving time decreases. As the particles have the smallerthreshold electric field intensity, the driving time becomes shorter.

As shown in FIG. 4, when the absolute value of the electric fieldintensity with which particles start the migration from one substrate tothe other substrate is V_(L) and the absolute value of the electricfield intensity with which all the particles end the migration from onesubstrate to the other substrate is V_(H), the threshold electric fieldintensity varies due to the driving energy for causing particles tomigrate. As the driving energy decreases, the threshold electric fieldintensity also decreases. For example, it is assumed that the thresholdcharacteristic of magenta particles M is a threshold characteristic whenthe driving energy is A as shown in FIG. 4 and is the thresholdcharacteristic 50M shown in FIG. 2. For example, when the driving energyis set to the driving energy B shown in FIG. 4 by fixing the voltagevalue and shortening the voltage application time, the driving energy Bis smaller than the driving energy A and thus the thresholdcharacteristic is shifted from the threshold characteristic 50M to thethreshold characteristic 50M′ as shown in FIG. 2. As shown in FIG. 3,the characteristic indicating the relationship between the electricfield intensity of the magenta particles M and the driving time of theparticles is the same as the characteristic 52M′. The driving energy ofone type of particles varies with the variation in driving energy of theother type of particles. For example, when the driving energy causingthe magenta particles M to migrate decreases, the driving energy causingthe cyan particles C to migrate also decreases like a chain reaction.

FIG. 5 illustrates the relationship between the electric field intensityand the driving speed of each type of particles. In the drawing, thecharacteristic of the magenta particles M is represented by 54M, thecharacteristic when the threshold characteristic of the magentaparticles M is shifted is represented by 54M′, and the characteristic ofthe cyan particles C is represented by 54C. As shown in the drawing, thedriving speed of the cyan particles C having a smaller thresholdelectric field intensity is higher than that of the magenta particles M.

In the example shown in FIG. 2, even when the threshold characteristicof the magenta particles M is shifted to the characteristic 50M′, theelectric field intensity V_(CH) with which the cyan particles C end themigration to the rear substrate 2 is smaller than the electric fieldintensity V_(ML)′ with which the magenta particles M start the migrationfrom the rear substrate 2 to the display substrate 1, whereby a mixedcolor is not generated and the driving time is shortened.

On the contrary, as shown in FIG. 6, when the threshold characteristic50M′ crosses the threshold characteristic 50C of the cyan particles C,that is, when the threshold electric field intensity V_(ML′) of themagenta particles M is smaller than the threshold electric fieldintensity V_(CH) of the cyan particles C, and for example, when thethreshold electric field intensity V_(CH) is applied across thesubstrates so as to drive the cyan particles C, the magenta particles Mmay also migrate to cause a mixed color. The magenta particles M may bedriven under such conditions that a mixed color is not caused dependingon the display density of the cyan particles C.

In this exemplary embodiment, the driving conditions of the magentaparticles M are set so that the driving time is shortened in a rangewhere a mixed color is not caused.

First, a basic driving procedure when the color of the particles isdisplayed in gray scales, that is, when the color density of theparticles is adjusted will be described.

When a color is displayed in gray scales, the driving procedurebasically includes a first stroke in which all the particles migrate toone substrate and a second stroke in which particles migrate from onesubstrate to the other substrate depending on the gray scale.

Specifically, for example, as shown in FIG. 7A, by applying a voltagecausing all the magenta particles M to migrate to the display substrate1 to the display electrode 3, all the magenta particles M are caused tomigrate to the display substrate 1 and all the cyan particles C arecaused to migrate to the rear substrate 2 (the first stroke of themagenta particles M).

As shown in FIG. 7B, a voltage causing the magenta particles Mcorresponding to the gray scale to remain on the display substrate 1side and causing the other magenta particles M to migrate to the rearsubstrate 2 is applied to the display electrode 3. Accordingly, themagenta particles M corresponding to the gray scale remain on thedisplay substrate 1 side, the other magenta particles M migrate to therear substrate 2, and all the cyan particles C migrate to the displaysubstrate 1 (the second stroke of the magenta particles M and the firststroke of the cyan particles C).

As shown in FIG. 7C, a voltage causing the cyan particles Ccorresponding to the gray scale to remain on the display substrate 1,causing the other cyan particles C to migrate to the rear substrate 2,and not causing the magenta particles M to migrate is applied to thedisplay electrode 3. Accordingly, the cyan particles C corresponding tothe gray scale remain in the display substrate 1 side and the othermagenta particles M migrate to the rear substrate 2 (the second strokeof the cyan particles C).

The particles may be driven in the procedure shown in FIGS. 8A to 8D.Specifically, as shown in FIG. 8A, the particles may be driven in thesame way as shown in FIG. 7A (the first stroke of the magenta particlesM). Then, as shown in FIG. 8B, the particles may be driven in the sameway as shown in FIG. 7B (the second stroke of the magenta particles M) .Then, as shown in FIG. 8C, a voltage causing all the cyan particles C tomigrate to the rear substrate 2 and not causing the magenta particles Mto migrate may be applied to the display electrode 3 (the first strokeof the cyan particles C). Subsequently, as shown in FIG. 8D, a voltagecausing the cyan particles C corresponding to the gray scale to migrateto the display substrate 1 and not causing the magenta particles M tomigrate may be applied to the display electrode 3 (the second stroke ofthe cyan particles C).

The procedures shown in FIGS. 7 and 8 are only examples and theinvention is not limited to the examples. For example, all the magentaparticles M may be first caused to migrate to the rear substrate 2, allthe cyan particles C may be caused to migrate to the display substrate1, the magenta particles M corresponding to the gray scale may be causedto migrate to the display substrate 1, all the cyan particles C may becaused to migrate to the rear substrate 2, and then the cyan particles Ccorresponding to the gray scale may be caused to migrate to the displaysubstrate 1.

The specific driving procedure will be described below. FIG. 9 shows thethreshold characteristics which are changed by fixing the voltage valueof a voltage, which is applied at the time of causing the magentaparticles M to migrate, and changing the voltage application time.

In FIG. 9, the threshold characteristics of the magenta particles M arerepresented by V_(thM3), V_(thM2), and V_(thM1) and the thresholdcharacteristic of the cyan particles C is represented by V_(thC). Thevoltage value of a voltage applied to the display electrode 3 in thefirst stroke of the magenta particles M when the display density of themagenta particles M is set to D_(M3) (the highest density) isrepresented by −V_(M3), the voltage value of a voltage applied to thedisplay electrode 3 in the second stroke of the magenta particles M (thefirst stroke of the cyan particles C) is represented by V_(M3), thevoltage value of a voltage applied to the display electrode 3 when thedisplay density of the cyan particles C is set to D_(C3) (the highestdensity) in the second stroke of the cyan particles C is represented by−V_(C3), the voltage value of a voltage applied to the display electrode3 when the display density of the cyan particles C is set to D_(C2) isrepresented by −V_(C2), and the voltage value of a voltage applied tothe display electrode 3 when the display density of the cyan particles Cis set to D_(C1) is represented by −V_(C1).

FIG. 10 shows the relationship between the threshold characteristicsV_(thM3), V_(thM2), and V_(thM1) and the driving energy of the magentaparticles M. Here, the driving energy means a voltage application timewhen a voltage of the voltage value V_(M3) is applied to the displayelectrode 3. As shown in FIG. 10, the threshold characteristic V_(thM3)is a threshold characteristic when a voltage of the voltage value V_(M3)and the voltage application time t_(M33) is applied to the displayelectrode 3. The threshold characteristic V_(thM2) is a thresholdcharacteristic when a voltage of the voltage value V_(M3) and thevoltage application time t_(M32) is applied to the display electrode 3.The threshold characteristic V_(thM1) is a threshold characteristic whena voltage of the voltage value V_(M3) and the voltage application timet_(M31) is applied to the display electrode 3. As shown in FIG. 10, thefollowing conditional expression is satisfied: t_(M33)>t_(M32)>t_(M31).

FIG. 11 shows the relationship between the threshold characteristics andthe density of the cyan particles C when the density of the magentaparticles M is set to D_(M3). As shown in FIG. 9, the thresholdcharacteristic V_(thC) of the cyan particles C crosses the thresholdcharacteristics V_(thM2) and V_(thM1) of the magenta particles M.Accordingly, when the density of the cyan particles C is equal to orgreater than D_(C2) and V_(thM2) and V_(thM1) are used as the thresholdcharacteristics of the magenta particles M, a mixed color may begenerated as shown in FIG. 11.

On the other hand, when a mixed color is not generated, it is preferablethat the driving time, that is, the voltage application time, is asshort as possible. Accordingly, as shown in FIG. 11, when the density ofthe cyan particles C is set to D_(C0) or D_(C1), V_(thM1) with which themixed color is not generated and the voltage application time isshortened is selected as the threshold characteristic of the magentaparticles M and the voltage application time is set to t_(M31).

When the density of the cyan particles C is set to D_(C2), V_(thM2) withwhich the mixed color is not generated and the voltage application timeis most shortened is selected as the threshold characteristic of themagenta particles M and the voltage application time is set to t_(M32).

When the density of the cyan particles C is set to D_(C3), V_(thM3) isselected as the threshold characteristic of the magenta particles M andthe voltage application time is set to t_(M33).

Specifically, table data indicating the relationship between the densityof the cyan particles C and the voltage application time which is theshortest at the time of driving the magenta particles M in the secondstroke without generating a mixed color may be stored in the nonvolatilememory 40D in advance for each density of the magenta particles M, thevoltage application time corresponding to the density of the cyanparticles C may be read from the table data corresponding to the densityof the magenta particles M, and the read voltage application time may beinstructed to the voltage application unit 30.

FIGS. 12A to 12C show a specific voltage applying procedure.

As shown in FIG. 12A, when the density of the magenta particles M is setto D_(M3) and the density of the cyan particles C is set to D_(C3) , avoltage of the voltage value −V_(M3) and the voltage application timet_(M33) is first applied to the display electrode 3 as the first strokeof the magenta particles M. Accordingly, all the magenta particles Mmigrate to the rear substrate 2 and all the cyan particles C migrate tothe display substrate 1.

A voltage of the voltage value +V_(M3) and the voltage application timet_(M33) is applied to the display electrode 3 as the second stroke ofthe magenta particles M and the first stroke of the cyan particles C.Accordingly, the magenta particles M corresponding to the densityD_(M3), that is, all the magenta particles M, migrate to the displaysubstrate 1 and all the cyan particles C migrate to the rear substrate2.

A voltage of the voltage value −V_(C3) and the voltage application timet_(C) corresponding to the density D_(C3) of the cyan particles C isapplied to the display electrode 3 as the second stroke of the cyanparticles C. Accordingly, the cyan particles C corresponding to thedensity D_(C3), that is, all the cyan particles C, migrate to thedisplay substrate 1.

As shown in FIG. 12B, when the density of the magenta particles M is setto D_(M3) and the density of the cyan particles C is set to D_(C2), avoltage of the voltage value −V_(M3) and the voltage application timet_(M33) is first applied to the display electrode 3 as the first strokeof the magenta particles M. Accordingly, all the magenta particles Mmigrate to the rear substrate 2 and all the cyan particles C migrate tothe display substrate 1.

A voltage of the voltage value +V_(M3) and the voltage application timet_(M32) is applied to the display electrode 3 as the second stroke ofthe magenta particles M and the first stroke of the cyan particles C.Accordingly, the magenta particles M corresponding to the densityD_(M3), that is, all the magenta particles M, migrate to the displaysubstrate 1 and all the cyan particles C migrate to the rear substrate2.

A voltage of the voltage value −V_(C2) and the voltage application timet_(C) corresponding to the density D_(C2) of the cyan particles C isapplied to the display electrode 3 as the second stroke of the cyanparticles C. Accordingly, the cyan particles C corresponding to thedensity D_(C2) migrate to the display substrate 1.

As shown in FIG. 12C, when the density of the magenta particles M is setto D_(M3) and the density of the cyan particles C is set to D_(C1), avoltage of the voltage value −V_(M3) and the voltage application timet_(M33) is first applied to the display electrode 3 as the first strokeof the magenta particles M. Accordingly, all the magenta particles Mmigrate to the rear substrate 2 and all the cyan particles C migrate tothe display substrate 1.

A voltage of the voltage value +V_(M3) and the voltage application timet_(M31) is applied to the display electrode 3 as the second stroke ofthe magenta particles M and the first stroke of the cyan particles C.Accordingly, the magenta particles M corresponding to the densityD_(M3), that is, all the magenta particles M, migrate to the displaysubstrate 1 and all the cyan particles C migrate to the rear substrate2.

A voltage of the voltage value −V_(C1) and the voltage application timet_(C) corresponding to the density D_(C1) of the cyan particles C isapplied to the display electrode 3 as the second stroke of the cyanparticles C. Accordingly, the cyan particles C corresponding to thedensity D_(C1) migrate to the display substrate 1.

An example where the density of the magenta particles M is set to D_(M1)will be described below.

FIG. 13 shows the threshold characteristics of the magenta particles Mand the cyan particles C. The threshold characteristics of the particlesare the same as shown in FIG. 9. In FIG. 13, the voltage value of thevoltage applied to the display electrode 3 in the first stroke of themagenta particles M is represented by +V_(M3), the voltage values of thevoltage applied to the display electrode 3 in the second stroke of themagenta particles M (the first stroke of the cyan particles C) arerepresented by −V_(M31), −V_(M21), and −V_(M11), the voltage value ofthe voltage applied to the display electrode 3 when the display densityof the cyan particles C is set to D_(C0) (the lowest density) in thesecond stroke of the cyan particles C is represented by +V_(C), thevoltage value of the voltage applied to the display electrode 3 when thedisplay density of the cyan particles C is set to D_(C1) is representedby +V_(C1), and the voltage value of the voltage applied to the displayelectrode 3 when the display density of the cyan particles C is set toD_(C2) is represented by +V_(C2).

FIG. 14 shows the relationship between the threshold characteristics andthe density of the cyan particles C when the density of the magentaparticles M is set to D_(M1). As shown in FIG. 13, the thresholdcharacteristic V_(thC) of the cyan particles C crosses the thresholdcharacteristics V_(thM2) and V_(thM1) of the magenta particles M.Accordingly, when the density of the cyan particles C is equal to orless than D_(C1) and V_(thM2) and V_(thM1) are used as the thresholdcharacteristics of the magenta particles M, a mixed color may begenerated as shown in FIG. 14.

On the other hand, when a mixed color is not generated, it is preferablethat the driving time, that is, the voltage application time, is asshort as possible. Accordingly, as shown in FIG. 14, when the density ofthe cyan particles C is set to D_(C2) or D_(C3) V_(thM1) with which themixed color is not generated and the voltage application time isshortened is selected as the threshold characteristic of the magentaparticles M and the voltage application time is set to t_(M31).

When the density of the cyan particles C is set to D_(C1), V_(thM2) withwhich the mixed color is not generated and the voltage application timeis most shortened is selected as the threshold characteristic of themagenta particles M and the voltage application time is set to t_(M32).

When the density of the cyan particles C is set to D_(C0), V_(thM3) isselected as the threshold characteristic of the magenta particles M andthe voltage application time is set to t_(M33).

FIG. 15 shows a specific voltage applying procedure when the density ofthe magenta particles M is set to D_(M1) and the density of the cyanparticles C is set to D_(C0).

As shown in FIG. 15, when the density of the magenta particles M is setto D_(M1) and the density of the cyan particles C is set to D_(C0), avoltage of the voltage value +V_(M3) and the voltage application timet_(M33) is first applied to the display electrode 3 as the first strokeof the magenta particles M. Accordingly, all the magenta particles Mmigrate to the display substrate 1 and all the cyan particles C migrateto the rear substrate 2.

A voltage of the voltage value −V_(M31) and the voltage application timet_(M33) is applied to the display electrode 3 as the second stroke ofthe magenta particles M and the first stroke of the cyan particles C.Accordingly, the magenta particles M corresponding to the density D_(M1)remain on the display substrate 1 side, the other magenta particles Mmigrate to the rear substrate 2, and all the cyan particles C migrate tothe display substrate 1.

A voltage of the voltage value +V_(C) and the voltage application timet_(C) corresponding to the density D_(C0) of the cyan particles C isapplied to the display electrode 3 as the second stroke of the cyanparticles C. Accordingly, all the cyan particles C migrate to thedisplay substrate 1.

As shown in FIG. 16A, when the density of the magenta particles M is setto D_(M1) and the density of the cyan particles C is set to D_(C1), avoltage of the voltage value +V_(M3) and the voltage application timet_(M33) is first applied to the display electrode 3 as the first strokeof the magenta particles M. Accordingly, all the magenta particles Mmigrate to the display substrate 1 and all the cyan particles C migrateto the rear substrate 2.

A voltage of the voltage value −V_(M31) and the voltage application timet_(M32) is applied to the display electrode 3 as the second stroke ofthe magenta particles M and the first stroke of the cyan particles C.Accordingly, the magenta particles M corresponding to the density D_(M1)remain on the display substrate 1 side, the other magenta particles Mmigrate to the rear substrate 2, and all the cyan particles C migrate tothe display substrate 1.

A voltage of the voltage value +V_(C1) and the voltage application timet_(C) corresponding to the density D_(C1) of the cyan particles C isapplied to the display electrode 3 as the second stroke of the cyanparticles C. Accordingly, the cyan particles C corresponding to thedensity D_(C1) remain on the display substrate 1 side and the other cyanparticles C migrate to the rear substrate 2.

As shown in FIG. 17A, when the density of the magenta particles M is setto D_(M1) and the density of the cyan particles C is set to D_(C2), avoltage of the voltage value +V_(M3) and the voltage application timet_(M33) is first applied to the display electrode 3 as the first strokeof the magenta particles M. Accordingly, all the magenta particles Mmigrate to the display substrate 1 and all the cyan particles C migrateto the rear substrate 2.

A voltage of the voltage value −V_(M31) and the voltage application timet_(M31) is applied to the display electrode 3 as the second stroke ofthe magenta particles M and the first stroke of the cyan particles C.Accordingly, the magenta particles M corresponding to the density D_(M1)remain on the display substrate 1 side, the other magenta particles Mmigrate to the rear substrate 2, and all the cyan particles C migrate tothe display substrate 1.

A voltage of the voltage value +V_(C2) and the voltage application timet_(C) corresponding to the density D_(C2) of the cyan particles C isapplied to the display electrode 3 as the second stroke of the cyanparticles C. Accordingly, the cyan particles C corresponding to thedensity D_(C2) remain on the display substrate 1 side and the other cyanparticles C migrate to the rear substrate 2.

When the density of the cyan particles C is D_(C1) and V_(thM2) isselected as the threshold characteristic of the magenta particles M, amixed color is not generated. Accordingly, as shown in FIG. 16B, avoltage of the voltage value +V_(M3) and the voltage application timet_(M32) may be applied to the display electrode 3 as the first stroke ofthe magenta particles M. A voltage of the voltage value−V_(M21)(|V_(M21)|<|V_(M31)|) and the voltage application time t_(M22)(>t_(M32)) may be applied to the display electrode 3 as the secondstroke of the magenta particles M.

When the density of the cyan particles C is D_(C2) and V_(thM2) isselected as the threshold characteristic of the magenta particles M, amixed color is not generated. Accordingly, as shown in FIG. 17B, avoltage of the voltage value +V_(M3) and the voltage application timet_(M32) may be applied to the display electrode 3 as the first stroke ofthe magenta particles M. A voltage of the voltage value−V_(M21)(|V_(M21)|<|V_(M31)|) and the voltage application time t_(M21)(>t_(M31)) may be applied to the display electrode 3 as the secondstroke of the magenta particles M.

When the density of the cyan particles C is D_(C2) and V_(thM1) isselected as the threshold characteristic of the magenta particles M, amixed color is not generated. Accordingly, as shown in FIG. 17C, avoltage of the voltage value +V_(M3) and the voltage application timet_(M31) may be applied to the display electrode 3 as the first stroke ofthe magenta particles M. A voltage of the voltage value−V_(M11)(|V_(M11)|<|V_(M21)|) and the voltage application time t_(M11)(>t_(M21)) may be applied to the display electrode 3 as the secondstroke of the magenta particles M.

The control performed by the CPU 40A of the control unit 40 will bedescribed below with reference to the flowchart shown in FIG. 18.

First, in step S10, image information of an image to be displayed on thedisplay medium 100 is acquired from an external device not shown, forexample, via the I/O 40E.

In step S12, the voltage value and the voltage application time of thevoltage applied in the first stroke of the magenta particles M are setin the voltage application unit 30. For example, when the density of themagenta particles M is D_(M3) and the density of the cyan particles C isD_(C3), −V_(M3) is set as a predetermined voltage value and t_(M33) isset as a predetermined voltage application time, as shown in FIG. 12A.

In step S14, the voltage value and the voltage application time of thevoltage applied in the second stroke of the magenta particles M (thesecond stroke of the cyan particles C) are set in the voltageapplication unit 30. Specifically, the table data corresponding to thedensity of the magenta particles M, that is, the table data indicatingthe relationship between the density of the cyan particles C and thevoltage application time which is the shortest at the time of drivingthe magenta particles M in the second stroke without generating a mixedcolor, is read from the nonvolatile memory 40D. The voltage applicationtime at the time of driving the magenta particles M in the second strokecorresponding to the density of the cyan particles C is set on the basisof the read table data.

For example, as shown in FIG. 12A, when the density of the magentaparticles M is D_(M3) and the density of the cyan particles C is D_(C3),the table data corresponding to the density D_(M3) of the magentaparticles M, the voltage application time t_(M33) corresponding to thedensity D_(C3) of the cyan particles C is read from the table data, andthe read data is set in the voltage application unit 30. Regarding thevoltage value, +V_(M3) is set as the predetermined voltage value, asshown in FIG. 12A.

In step S16, the voltage value and the voltage application time of thevoltage applied in the second stroke of the cyan particles C is set inthe voltage application unit 30. Specifically, for example, as shown inFIG. 12A, when the density of the magenta particles M is D_(M3) and thedensity of the cyan particles C is D_(C3), the predetermined voltagevalue −V_(C3) and the predetermined voltage application time t_(C)corresponding to the density D_(C3) of the cyan particles C are set inthe voltage application unit 30.

In this exemplary embodiment, it has been stated that the thresholdcharacteristic of the magenta particles M is changed by fixing thevoltage value and changing the voltage application time. However, thethreshold characteristic of the magenta particles M may be changed byfixing the voltage application time and changing the voltage value.

In this exemplary embodiment, it has been stated that the particlegroups include two groups of the magenta particles M and the cyanparticles C. However, the number of types of particles may be three ormore. For example, the invention can be applied to the case where theparticle groups include three types of magenta particles M, cyanparticles C, and yellow particles Y.

EXAMPLES

Examples of the invention will be described below.

Production of Non-Charged White Particles

5 part by mass of 2-vinyl naphthalene (made by Nippon Steel ChemicalCo., Ltd.), 5 part by mass of Silaplane FM-0721 (made by ChissoCorporation), 0.3 part by mass of lauroyl peroxide as an initiator (madeby Wako Pure Chemical Industries Ltd.), and 20 part by mass of siliconeoil KF-96L-1CS (made by Shin-Etsu Chemical Co., Ltd.) are added to a 100ml three-necked flask having a reflux condenser tube attached thereto,the resultant is subjected to a bubbling process using nitrogen gas for15 minutes, and the resultant is then subjected to a polymerizationprocess at 65° C. for 24 hours in the atmosphere of nitrogen, wherebywhite particles are produced.

The resultant white particles were refined by repeatedly performing aparticle precipitation process using a centrifugal separator and awashing process using silicone oil. In this way, a dispersion liquid inwhich white particles are dispersed and of which the particle solidcontent is 40 mass % is produced. The volume average particle diameter(measured with FPAR-1000 made by Otsuka Electronics Co., Ltd.) of theproduced white particles is 550 nm.

Production of Cyan Migration Particles C1, Positive Charging, LowThreshold

95 part by mass of Silaplane FM-0711 (made by Chisso Corporation) , 3part by mass of methyl methacrylate, and 2 part by mass of glycidylmethacrylate and are mixed with 50 part by mass of silicone oil(KF-96L-2CS made by Shin-Etsu Chemical Co., Ltd.), 0.5 part by mass ofAIBN (2,2-azobis isobutyl nitrile) as a polymerization initiator isadded thereto, and the resultant is polymerized, whereby reactivesilicone-based polymer A (reactive dispersant) having an epoxy group isproduced.

Then, copolymer of N-vinyl pyrrolidone and N,N-diethylaminoethylacrylatewith a mass ratio of 9/1 is synthesized by the known radical solutionpolymerization.

Then, 3 part by mass of a 10 mass % aqueous solution of the copolymer ismixed with 1 part by mass of a water-dispersed pigment solution(Unisperse Cyan, pigment content of 26 mass %, made by Ciba Co.), themixed solution is mixed with 10 part by mass of a 3 mass % siliconesolution of reactive silicone-based polymer A, and the resultant isstirred by the use of an ultrasonic grinder for 10 minutes, whereby asuspension in which an aqueous solution containing polymer and pigmentis dispersed and emulsified in silicone oil is produced.

The suspension is depressurized (2 KPa) and heated (70° C.) to removemoisture therefrom, whereby a silicone oil dispersion liquid in whichcolored particles containing polymer and pigment are dispersed in thesilicone oil is obtained. The dispersion liquid is heated at 100° C. for3 hours and is caused to react with the reactive silicone-based polymerand thus to be bonded thereto. Then, butylbromide corresponding to 50mol % of N,N-diethylaminoethylacrylate in solid particles is added tothe dispersion liquid, the resultant is heated at 80° C. for 3 hours andis subjected to an amino group quaternizing process, and the resultantis refined by repeatedly performing a particle precipitation processusing a centrifugal separator and a washing process using silicone oil.In this way, a dispersion liquid in which colored particles containingcyan pigment are dispersed and of which the particle solid content is 4mass % is produced.

The volume average particle diameter (measured with FPAR-1000 made byOtsuka Electronics Co. , Ltd.) of the produced cyan particles is 680 nm.

Production of Magenta Migration Particles M1, Negative Charging, HighThreshold

19 part by mass of Silaplane FM-0725 (made by Chisso Corporation), 29part by mass of Silaplane FM-0721 (made by Chisso Corporation), 9 partby mass of methyl methacrylate (made by Wako Pure Chemical IndustriesLtd.), 5 part by mass of octofluoropentyl methacrylate (made by WakoPure Chemical Industries Ltd.), and 38 part by mass of hydroxyethylmethacrylate (made by Wako Pure Chemical Industries Ltd.) are mixed with300 part by mass of isopropyl alcohol (IPA), 1 part by mass of AIBN(2,2-azobis isobutyl nitrile) as a polymerization initiator is meltedtherein, and the resultant is polymerized in the nitrogen atmosphere at70° C. for 6 hours. The resultant product is refined using hexane as are-precipitation solvent and then dried, whereby silicone-based polymeris obtained.

0.5 part by mass of silicone-based polymer B is added to and melted in 9part by mass of isopropyl alcohol (IPA), 0.5 part by mass of magentapigment (Pigment Red 3090) made by Sanyo Color Works Ltd. is addedthereto, and the resultant is dispersed for 48 hours using zirconiaballs with a diameter of 0.5 mm, whereby a pigment-containing polymersolution is obtained.

3 part by mass of the pigment-containing polymer solution is taken outand is heated at 40° C., and 12 part by mass of silicone oil (KF-96L-2CSmade by Shin-Etsu Chemical Co., Ltd.) is dropped thereon little bylittle while applying ultrasonic waves thereto, whereby silicone-basedpolymer is extracted to the pigment surface. Thereafter, the resultantsolution is heated at 60° C. and depressurized and dried to evaporatethe IPA, whereby magenta particles in which silicone-based polymer isattached to the pigment surface are obtained.

The obtained magenta particles are refined by repeatedly performing aparticle precipitation process using a centrifugal separator and awashing process using silicone oil. In this way, a dispersion liquid inwhich colored particles containing magenta pigment are dispersed and ofwhich the particle solid content is 4 mass % is produced. The volumeaverage particle diameter (measured with FPAR-1000 made by OtsukaElectronics Co., Ltd.) of the produced magenta particles is 380 nm.

Adjustment of Mixture Solution of CM2 Particle System

The white particle dispersion liquid, the cyan particle dispersionliquid, and the magenta particle dispersion liquid are mixed at thefollowing ratio to produce a mixture solution of a CM2 particle system.

Mixture Ratio W:C:M=2:1:1 (wt %)

Manufacturing of Display Medium

ITO as an electrode is formed on a glass substrate of 50 mm×50 mm×1.1 mmas a surface substrate and a rear substrate with a thickness of 50 nm bythe use of a sputtering method, and fluorine resin (CYTOP made by AsahiGlass Co., Ltd.) is formed thereon with a thickness of 100 nm by the useof a spin coating method.

A sheet obtained by cutting out a 20 mm×20 mm square from the centralportion of a fluorine resin sheet of 50 mm×40 mm×50 μm is used as aspacer and is placed on the rear substrate.

The adjusted mixture solution of the CM2 particle system is injectedinto the square space formed at the central portion of the spacer.Thereafter, the surface substrate is brought into close contact with thespacer and both substrates are pressed and held with a double clip tobring the spacer into close contact with both substrates, whereby adisplay medium is manufactured.

Evaluation Method

A voltage is applied across electrodes of the manufactured displaymedium, reflected light therefrom is measured with a spectroscope(USB2000+ made by Ocean Optics Inc.), and display characteristics areevaluated. The threshold characteristics of the manufactured displaymedium are shown in FIG. 19.

Evaluation Result of Driving

As the first stroke of the magenta particles which are high-thresholdparticles, 15 V is applied to the manufactured display medium for 1second so as to set the display substrate as a positive electrode. Atthis time, the surface substrate is changed to magenta and the rearsubstrate is changed to cyan. A voltage is applied so as to set thedisplay substrate as a negative electrode as the second stroke of themagenta particles which are high-threshold particles and the firststroke of cyan particles which are low-threshold particles, whereby thedisplay substrate is changed to cyan and the rear substrate is changedto magenta. Subsequently, a voltage is applied so as to set the displaysubstrate as a negative electrode as the second stroke of cyan particleswhich are low-threshold particles.

The density of cyan particles, the driving condition in the secondstroke of magenta particles, and the mixed color has the relationshipshown in FIGS. 20 to 22. The voltage value and the voltage applicationtime of the voltage applied in the second stroke of the cyan particles Cand the density exhibit the relationship shown in FIG. 23.

FIGS. 20 and 21 show the results when the voltage value is fixed and thevoltage application time is changed, where the voltage value in FIG. 20is fixed to 15 V and the voltage value in FIG. 21 is fixed to 30 V. FIG.22 shows the result when the voltage application time is fixed and thevoltage value is changed.

The mixed color is evaluated using a color difference ΔE (the squareroot of the sum of squares of differences in L* axis, a* axis, b* axis)from displayed cyan in a state where no mixed color present. When ΔE<5,it is evaluated as no mixed color: ο. When ΔE≧5, it is evaluated asmixed color: X.

As can be seen from the comparison of the results shown in FIGS. 21 and22, it is possible to shorten the total driving time by fixing thevoltage value and changing the voltage application time.

In the past, the driving conditions in the second stroke of the magentaparticles M are fixed (the leftmost conditions in FIGS. 20 to 22). As aresult, it can be seen that the total driving time is longer than thatin the invention.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A display medium driver that controls a displaymedium including a pair of substrates, a dispersion medium that isenclosed between the substrates, a first particle group that isdispersed in the dispersion medium and that migrates by applying a firstvoltage having an absolute value that is equal to or greater than afirst threshold value across the substrates, and a second particlegroup, having a color different from the first particle group, that isdispersed in the dispersion medium and that migrates by applying asecond voltage having an absolute value that is equal to or greater thana second threshold value less than the first threshold value across thesubstrates, the display medium driver comprising: a setting unit thatsets a voltage value and voltage application time of the first voltagefrom a plurality of predetermined pairs of a voltage value and voltageapplication time of the first voltage when making the second particlegroup migrate by applying the second voltage after making the firstparticle group migrate by applying the first voltage, wherein thevoltage value and the voltage application time set by the setting unitare selected from pairs which does not make the first particle groupmigrate even if the second voltage is applied after the first voltage isapplied and the pair set by the setting unit has a lowest drive energyin the pairs which does not make the first particle group migrate; and avoltage application unit that first applied the first voltage set by thesetting unit across the substrates and then applies the second voltageacross the substrates.
 2. The display medium driver according to claim1, wherein the setting unit fixes the voltage value of the first voltageand changes the voltage application time of the first voltage dependingon a display density of the second particle group.
 3. A display devicecomprising: a display medium including a pair of substrates, adispersion medium that is enclosed between the substrates, a firstparticle group that is dispersed in the dispersion medium and thatmigrates by applying a first voltage having an absolute value that isequal to or greater than a first threshold value across the substrates,a second particle group, having a color and charged polarity differentfrom the first particle group, that is dispersed in the dispersionmedium and that migrates by applying a second voltage having an absolutevalue that is equal to or greater than a second threshold value lessthan the first threshold value across the substrates, a setting unitthat sets a voltage value and voltage application time of the firstvoltage from a plurality of predetermined pairs of a voltage value andvoltage application time of the first voltage when making the secondparticle group migrate by applying the second voltage after making thefirst particle group migrate by applying the first voltage, wherein thevoltage value and the voltage application time set by the setting unitare selected from pairs which does not make the first particle groupmigrate even if the second voltage is applied after the first voltage isapplied and the pair set by the setting unit has a lowest drive energyin the pairs which does not make the first particle group migrate; and avoltage application unit that first applies the first voltage set by thesetting unit across the substrates and then applies the second voltageacross the substrates.